Polarizing plates (polarizing films) for use in liquid crystal displays and the like are each usually formed from a substrate (optical film) of excellent transparency and a polarizing film (polarizer). The polarizing plates may be formed from a film (retardation film) obtained by stretching an optical film and having a function of imparting retardation to transmitted light and a polarizing film.
As the optical films used for substrates or retardation films of the polarizing plates, polycarbonate films, polyester films, acetate films, etc. have been heretofore used. Polarizing plates using the polycarbonate films or the polyester films, however, have a large photoelastic coefficient and sometimes change retardation to be imparted to transmitted light because of a little change of stress or the like. The acetate films have low heat resistance and high water absorption, so that polarizing plates using them have a problem that the polarizing plates are liable to be distorted depending upon the environment where the plates are used.
On the other hand, norbornene resins have been paid attention as materials of various optical parts because of their excellent transparency, heat resistance and chemical resistance. In Japanese Patent Laid-Open Publication No. 6-51117/1994, a polarizing film (polarizing plate) wherein a norbornene resin sheet is laminated as a protective film on a polarizing film has been proposed.
The norbornene resins, however, have bad adhesion properties to other resin materials, so that it was difficult to produce polarizing plates using norbornene resin films. Further, there is a problem that delamination is liable to take place when they are used for a long period of time. Moreover, in order to improve scratch resistance and antireflection properties, one surface of the polarizing plate is sometimes subjected to surface treatment such as hard coating treatment, and also in this case, there is a problem that separation takes place in the long-term use. On this account, development of polarizing plates using norbornene resin films and having excellent adhesion properties has been eagerly desired.